Embodiments of the inventive concept relate generally to semiconductor memories and, more particularly, to nonvolatile memory systems and related methods of operation.
Semiconductor memory devices can be roughly divided into two categories according to whether they retain stored data when disconnected from power. These categories include volatile memory devices, which lose stored data when disconnected from power, and nonvolatile memory devices, which retain stored data when disconnected from power. Examples of volatile memory devices include dynamic random access memory (DRAM) and static random access memory (SRAM), and examples of nonvolatile memory devices include read only memory (ROM), magnetoresistive random access memory (MRAM), resistive random access memory (RRAM), and flash memory.
Flash memory is an especially popular form of nonvolatile memory due to attractive features such as relatively high storage density, efficient performance, low cost per bit, and an ability to withstand physical shock. Some flash memories include charge trap flash (CTF) memory cells. A CTF memory cell stores charges in a charge storage layer to represent a program state.
A threshold voltage distribution of CTF memory cells may vary due to charges flowing into a channel after the CTF memory cells are programmed. This physical characteristic may distort stored data by changing the threshold voltage distributions of stored data. However, such distortion can be compensated for by controlling and/or monitoring program time of memory cells. For instance, if the threshold voltage distribution of a group of memory cells is deemed to be distorted based on a monitored program time of those memory cells, certain parameters of read operations can be adjusted to take into account the distortion. Unfortunately, the control and/or monitoring of program time of the memory cells may require a separate storage area and may also increase the amount of time required to perform read operations.